It is reported that a prompt increase in the arterial ketone body ratio (acetoacetate/beta-hydroxybutyrate), which reflects the mitochondrial redox state of the liver graft, is a decisive prerequisite for graft survival in clinical liver transplantation. To contrast the rôle of hepatic mitochondrial redox state in partial hepatectomy with that in hepatic replacement, the changes in the ketone body ratio were investigated in 107 cases of hepatectomy. The ketone body ratio in uneventful cases (n = 70) in the first three days after hepatectomy was significantly higher than that in eventful cases. In the uneventful cases, the ketone body ratios were all increased to above 1.0 within two days after hepatectomy, except in diabetics, whose preoperative values did not reach 1.0 under oral glucose load. However, 20 (22.7%) out of 88 cases whose ketone body ratios promptly increased after hepatectomy had mild to moderate complications thereafter. It is suggested that the recovery of hepatic mitochondrial redox state is also a prerequisite in partial hepatectomy, where a reduced and often damaged liver confronts systemic metabolic load.